A bicycle equipped with a speed shifter such as a derailleur and a hub gear is commonly equipped with a speed change operation assembly connected to the speed shifter via a control cable. Desired speed change operation is performed by operating the speed change operation assembly. In such a bicycle it is desirable for a rider to be able to know easily what speed stage he is using. Thus, a conventional speed change operation assembly has a scale showing the speed positions such as first gear and second gear.
Recently, bicycle speed shifter tends to have an increasing number of speed stages. Especially, a sports type bicycle is now commonly equipped with a front speed shifter having two or a greater number of speed stages, and with a rear speed shifter having three or a greater number of speed stages. However, such a bicycle having a front and a rear speed shifters is only equipped with a pair of speed change operation assemblies for respective front and rear speed shifters, and each speed change operation assembly is provided with a scale solely showing the speed stages of its own speed shifter.
This type of conventional arrangement in which each of the two speed change operation assemblies only has an individual scale for its own speed stages has following problems:
Reference is now made to FIG. 15, which shows an enlarged plan view of a primary portion of a bicycle equipped with a front derailleur (not shown) capable of shifting a chain 4A between three front gears F1 through F3, and a rear derailleur (not shown) capable of shifting a chain 4A between six rear gears R1 through R6. In this bicycle, chain 4A currently engages with front gear F1 and rear gear R4. If a speed change operation to a lower speed stage is to be made, it is more desirable to shift a front portion of chain 4A to the front gear F2 than shifting a rear portion of chain 4A to the rear gear R5 or R6, because as shown in the phantom line in FIG. 12, shifting the chain 4A to the rear gear R5 or R6 will increase an engagement angle .theta. of chain 4A, resulting in noise or easy disengagement of chain due to poor engagement between the chain and the gears. In addition, the service life of chain 4A will be shortened because the chain 4A is subjected to lateral forces other than tension.
There is another problem if the rear portion of chain 4A is shifted to the rear gear R6: A speed change operation to a further lower speed stage can no longer be achieved by operating the rear derailleur, and therefore, a front portion of the chain 4A must be shifted to the front gear F2. If there is still further need to shift down, the only option is to shift the front portion of chain 4A to the front gear F3. This type of speed change operation practice only makes use of large gear ratios between front gears, making unavailable the access to more advantageous 6 speed options provided by the rear gears R1 through R6 having a smaller gear ratios for finer speed control.
As exemplified in the above, in a bicycle equipped with a front speed shifter and a rear speed shifter, there are certain favorable and unfavorable combinations of a front speed stage and a rear speed stage.
However, in a conventional bicycle, the front speed stage and the rear speed stage can only be confirmed individually. The rider cannot know easily how he can advantageously combine a front speed stage with a rear speed stage. Even if he knows favorable combinations, it is still very difficult for him to make such a setting quickly while riding on a bicycle.